Association between weekly exercise minutes and resting IL-6 in adults with chronic spinal cord injury: findings from the fracture risk after spinal cord injury exercise study

Study design: Cross-sectional study. Objective: To assess associations between weekly aerobic exercise minutes and resting interleukin-6 (IL-6), C-reactive protein (CRP), or leptin levels in adults with chronic spinal cord injury (SCI). Setting: Three hundred and forty-four community-dwelling men and women with SCI duration of > 1 year. Methods: CRP, IL-6, and leptin levels were quantified by ultra-sensitive enzyme-linked immunoassay. Smoking, medication use, comorbidities, and aerobic exercise minutes per week were assessed by self-reported questionnaire. Body composition was determined by whole-body dual-energy X-ray absorptiometry. Generalized linear models were used to assess associations. Results: In multivariable modeling, resting IL-6 levels were 0.001 pg/mL lower for every 1 min of weekly aerobic exercise. IL-6 levels increased with increasing android-to-gynoid fat ratio, in active/ever smokers compared to never smokers, and in individuals with skin pressure injuries compared to those without. IL-6 levels were lower in active ibuprofen users compared to nonusers. We found no association between weekly exercise minutes and CRP or leptin when designing similar models. Conclusions: Increasing aerobic exercise minutes is associated with lower IL-6 levels in adults with chronic SCI when considering body composition, smoking, skin pressure injuries, and ibuprofen use. CRP and leptin did not demonstrate an association with exercise when considering the similar variables. The use of these biomarkers in assessing the therapeutic value of future exercise-related interventions will be paramount for meaningful health improvement among those with SCI. Although a large, prospective dataset, this cross-sectional study cannot assign causation. Future prospective studies are needed to confirm these findings.